We report a single-beam triaxial atomic magnetometer based on cross bias magnetic field. Based on Bloch equation, the theory of single-beam scheme to achieve triaxial magnetic field detection is studied. To achieve triaxial magnetic field detection, the method of using cross bias magnetic field to rotate the atomic spin polarization direction is proposed and experimentally verified. By using only one single modulation magnetic field, it is possible to suppress low frequency noise and avoid the problem of magnetic field cross-talk. The experimental results show that the system response bandwidth to the magnetic field along X-axis is 90 Hz and the system sensitivity is 21 fT/(Hz^1/2) under the zero-field condition. The system response bandwidth to the magnetic field along Y-axis is 130 Hz and the system sensitivity is 26 fT/(Hz^1/2) when a bias magnetic field of 34 nT is applied in the Z-axis. The system response bandwidth to the magnetic field along Z-axis is 128 Hz and the system sensitivity is 29 fT/(Hz^1/2) when a bias magnetic field of 38 nT is applied in the Y-axis. The proposed triaxial atomic magnetometer has the advantages of small size, simple structure and low fabrication cost, and is expected to be used in the biomedical and other fields.